The present invention relates to a cleaning and/or treatment device for cleaning and/or treating surfaces such as floors, pavements and carpets. The invention particularly relates to a cleaning and/or treatment device using cleaning/treatment solution, wherein the solution is recirculated and thereby used more than one time. The invention also relates to a process of cleaning and/or treating surfaces using such a device.
Cleaning devices such as floor scrubbers and carpet cleaners using detergent solutions comprising water and detergent (detergent solution is in the following referred to as solution) are well known in the art. Most of the known cleaning devices use the solution only once, and consequently use a lot of solution under operation. The general way of operating a floor scrubber or a carpet cleaning machine is firstly to prepare a solution. The solution is then placed in a clean solution tank of the machine, From the clean solution tank, the solution is fed to the surface (hard floor, carpet etc.) and spread onto said surface. The surface is cleaned using the dissolving power of the detergents, and may further be cleaned by mechanical means such as a brush. The mixture of dirt and solution is finally removed from the surface e.g. by using a squeegee and transported to a “dirty solution tank” of the machine. The dirty solution must then be disposed of (typically to the sewer). A new solution is prepared and filled into the machine, and the cleaning process may be continued.
As it appears from the above description, much operation time is required for emptying the dirty solution tank and refilling the cleaning device with fresh solution, Furthermore, cleaning devices using the solution only once, should either have a large supply tank or can only operate for a very short time. Another disadvantage of the above mentioned cleaning devices using solution only once is that a lot of solution comprising unused detergents is discarded into the environment which is both expensive and polluting to the environment. In order to avoid this problem, a number of cleaning devices having means for recirculating solution have been suggested.
A number of patent publications disclose different ways of recycling the solution in order to achieve more operational time and less discharge of dirty solution to the surrounding environment. The methods used are quite different from each other, and some of the methods have unwanted effects on the quality of cleaning, while still other methods require a lot of maintenance time.
U.S. Pat. No. 4,194,263 discloses a scrubber comprising a clean solution tank and a dirty solution tank A separator is placed between the clean solution tank and the dirty solution tank to separate the dirty solution into a sludge portion which is returned to the dirty solution tank, and a clean solution which is returned to the clean solution tank for being reused. The separator is a laminar flow tube settler.
A similar scrubber is known from U.S. Pat. No. 4,295,2443. In this scrubber, the separator has been replaced by a series (a box) of sedimentation chambers.
In GB 2,124,478A disclosing a similar scrubber, a separating system comprising a sedimentation chamber followed by centrifugation has been suggested.
EP 0 224 055 A2 discloses a similar cleaning device comprising a clean solution tank and a dirty solution tank. The two tanks are openly connected, and when passing from the dirty solution tank to the clean solution tank, solution has to pass a first filter with large mesh size and a fine filter for separating dirt from the solution.
In U.S. Pat. No. 5,535,476, a mobile cleaning apparatus with a clean solution tank and a dirty solution tank is disclosed. This apparatus includes a system of cleaning the dirty solution comprising a sieveplate in the dirty solution tank and a filter bag in the clean solution tank.
In U.S. Pat. No. 3,753,777, a method for cleaning surfaces is disclosed. In this method, a flocculant (polyelectrolytes) is added to the dirty solution in order to create “flocs of dirt” Thereafter, these flocs of dirt are removed using a sieve or a filter. Hereafter, the solution may be recycled. Adding polyelectrolytes (flocculants) to the solution will often cause less dissolving power of detergents present in the solution since these detergents often chemically bind to the flocculant, and thus cause either increased use of detergents or a less optimal cleaning result.
The main separation principals used for separating dirt and solution in the above described moving cleaning machines are sedimentation and filtration.
The “dirt” and debris present in the dirty solution are normally a mixture of particles having all shapes, regular or irregular, and typical densities varying from 0.1 to 10 g/cm3. For sedimentation to take place sedimentation time and physical conditions (rest) are important factors.
Sedimentation is not an effective separation technique for separating particles with specific gravities <1.00 g/m3.
For example, a 10 μm sphere (specific gravity 1.1 g/cm3) sinking in a slurry or “dirty water” solution (a low solids concentration water suspension with specific gravity of approximately 1.0 g/cm3) using Stokes law (anticipating laminar movement) results in a settling velocity Vs:Vs=D2*g*(pp,−pw,)/18*μw=5.45*10−6 m/sekThis means that such a sphere will require 1835 seconds to travel 1 cm. From this it can be concluded that the separator requires a residence time of the order of about 31 minutes. In the case where the dirty solution is a high solids concentration suspension, the residence time will increase further, due to the hindrance from the other solids in the solution. Addition of surface active materials, such as detergents, may further increase the sedimentation time. Solution consumption in floor scrubbers, for example, is of the order 1-10 l/min. Thus, the volume (size) of the separator unit becomes quite large and impractical for moving machines when small dirt particles (approximately 10 μm) must be removed. Practically, it is not possible to obtain a clear cleaned solution from a dirty solution by using sedimentation separation only. This will be shown later on in the section “Sedimentation of dirt”.
Using filters as described in the above apparatus and methods have other disadvantages. The filters in all the devices described in the above mentioned patent publications are simple filters having a relatively open mesh. Such filters will not stop all visible particles. By applying several such filters in series each having still finer mesh size the solution may become relatively clear as described in U.S. Pat. No. 5,331,713 (White Cons. Ind.), but all traditional filters, as used in the known cleaning devices will clog. In the 4-filter-system described in U.S. Pat. No. 5,331,713, the dirt is captured in the filter system, mid no regeneration of the filters is described. Such “in-depth filter types” require fluent replacement, even when the particle or “dirt” load in the dirty solution is relatively low. Filtration of high “dirt” loaded solutions is practically impossible.